Examples of general standards for wireless networks may include the IEEE (Institute of Electrical and Electronics Engineers) 802.11 standards.
For example, in IEEE 802.11a/g, an OFDM (Orthogonal Frequency Division Multiplexing) modulation method, which is a multi-carrier method, is adopted as a standard for wireless LANs. In the OFDM modulation method, transmission data is distributed and transmitted over a plurality of carriers having frequencies that are orthogonal. Thus, the band of each carrier is narrow, resulting in greatly increased frequency use efficiency and increased resistance to frequency-selective fading interference.
The IEEE 802.11a/g standards support modulation methods that achieve a communication speed up to 54 Mbps. However, a demand for wireless standards capable of providing higher bit rate as communication speed still exists. For example, in IEEE 802.11n, which is an extension of IEEE 802.11a/g, next generation wireless LAN standards are being developed for the development of high-speed wireless LAN technologies over 100 Mbps of effective throughput.
In IEEE 802.11n, the OFDM_MIMO method that utilizes OFDM as its primary modulation technique is used. MIMO (Multi-Input Multi-Output) communication is a technology for providing high-speed wireless communication using a plurality of spatially multiplexed spatial streams between a transmitter and a receiver each of which is provided with a plurality of antenna elements.
A transmitter distributes and sends transmission data over a plurality of streams using a plurality of antennas. A receiver spatially demultiplexes spatially multiplexed signals received by a plurality of antennas by performing signal processing using channel characteristics, and extracts a signal for each stream without crosstalk (see, for example, PTL 1). The MIMO communication method can increase the transmission capacity in accordance with the number of antennas without increasing the frequency band, and can improve communication speed.
Due to the increased speed of the physical layer, IEEE 802.11n offers communication up to 600 Mbps. However, this means that the instantaneous maximum data transmission value is 600 Mbps per second. In IEEE 802.11n, frame aggregation as a MAC layer function is standardized as a mechanism for improving throughput by increasing the data transmission time as well as increasing the speed of the physical layer.
In frame aggregation, a large number of packets are combined so that a large amount of data can be transmitted in a single frame transmission, and the proportion of the transmission time of data is increased to improve throughput. A-MPDU (Aggregate MAC Protocol Data Unit) illustrated in FIG. 29(a) and A-MSDU (Aggregate MAC Service Data Unit) illustrated in FIG. 29(b) are specified as types of packet aggregation.
The A-MSDU type is a type in which packets are aggregated on a per-MSDU basis, that is, portions subsequent to the MAC header of an MPDU are aggregated. The A-MPDU type is a type in which packets are aggregated on a per-MPDU basis. In an A-MPDU frame, an FCS (error-detecting code) can be added to each of the MPDUs contained therein. In an A-MPDU frame, further, the maximum value of data that can be aggregated is 64 Kbytes. In an A-MSDU frame, the over of the MAC header is lower. However, since the entire frame is a single MPDU, a single FCS (error-detecting code) is used for the entire frame and if a portion of the frame has failed, all the MSDUs are to be retransmitted. In an A-MSDU frame, further, the maximum value of data that can be aggregated is 8 Kbytes.